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A Week of Shock?

While the water is crystal clear, after a week the chlorine is not leveling. I am setting the shock level at 16 (based on 40 CYA), but after doing a drop test every night the FC still drops by a point or two. Sometimes I have CC, sometimes not.
Not able to brush the pool everyday, but every other day. Even got in the water to scrub the seam around the steps, under the ladder steps, around light, etc.
Some mornings I see a little evidence of brown along the vinyl seam on the pool floor, but not sure if just dust, pollen or dead algae. (Using a solar blanket.)

FC: 15
CC: 0.5
Ph: 7.6
TA: 100
CH: 123
CYA: 40

Do I need to bump the shock level to 20? (Saw in another post.) Right now I am going through bleach and a LOT of my TF-100 chemicals. R-0871 almost gone.

Re: A Week of Shock?

Aiming for an FC of 16 is correct, but you are also correct that you might see some benefit by shooting for 18 or even 20, although I wouldn't see a need to go beyond 20 ppm. This is because 16 ppm is where you need to hold it, consistently, to clear the pool of organics. Dosing the bleach for a little higher FC will ensure that you stay in the shock range for a bit longer. A sort of cushion. Depending on the contaminant load, your FC will start depleting as soon as you add sanitizer. FC of 16 is your minimum to shock and as soon as it hits 15, it's too low already.

When you are checking your overnight FC loss, you are making certain that you are doing both tests with no sunlight hitting the water, correct? This is important.

You mentioned that you aren't able to brush every day and this is understandable. Unfortunately, when shocking, you need to have at least a couple of days where you can really spend some time brushing and maintaining that FC level. Brushing helps expose things that are contaminating your pool to higher concentrations of sanitizer and they die more quickly because of it. Not being able to stay on top of it can really prolong the process.

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After reading your post again, I think that I need to clarify whether or not you are saying that you are losing your FC overnight, or throughout the course of the day. If you are losing FC overnight, then you aren't finished shocking. But if you are losing your FC during the day, then this is normal and a CC of 0.5 or less wouldn't indicate a need to shock.

Re: A Week of Shock?

Thanks for the post.
I'm testing for overnight drop, and losing FC during the night (and also the day, as to be expected).
I didn't realize that even when it drops to 15 that is too low.
I'll bump it up to 18 as a cushion and really keep after the brushing. (I have to prove to my wife that BBB works.)

Re: A Week of Shock?

Are you brushing the entire pool at least occasionally while at shock level? Algae can form bio-films on surfaces that are very difficult to kill. Brushing disrupts the bio-film and exposes the algae to chlorine so it can be killed. Look in obscure places for algae that is hiding from the chlorine, like underneath or inside stairs, inside the lighting niche, inside the auto fill float tank, etc. Of course, you might not have all, or any, of those places on your pool, but if you do they are places algae can hide and cause the symptom you describe.

Re: A Week of Shock?

Also, allow me to revise one of my suggestions that I made earlier. With regard to maintaining an FC of 16 during the shocking process, I don't want you to panic if the FC drops to below 16 and feel as though you must immediately run to the store to get more bleach. In spite of what I said earlier, an FC of 15 would not necessarily mean that superchlorination comes to a screeching halt. You are still shocking. It's just that based on study and experience of some very smart people around here, when the CYA in your water is X, an FC of Y is optimum for timely treatment. Does this make sense?

Re: A Week of Shock?

No confusion at all. I'm learning a lot here.
I lose about 2 during the day and 1 at night. CC usually shows itself as 0.5 every other day.
Yes, I brush the whole pool, and really feel it in my shoulders! I can sometimes see a small cloud of brown brush up in some spots, usually on the W and NW walls.
Just finished brushing and getting the FC to 18 (just in case). I just need to be more diligent this time and get it knocked out.

BTW, it makes me wonder how a pool company would deal with this. I can't imagine they would be out every day to brush test morning and night. Reason I ask is if I deploy again, my wife said she is hiring someone.